SECONDARY BATTERY AND METHOD FOR PREPARING THE SAME, AND ELECTRICAL APPARATUS
Provided are a secondary battery including an electrode sheet, the electrode sheet including: a current collector and an active material layer; the active material layer is provided on at least one surface of the current collector; the active material layer is divided into a first region and a second region in its thickness direction; the first region is located in a direction close to the surface of the current collector, the thickness of the first region accounts for ½ of the thickness of the active material layer, the binder content in the first region is denoted as A; the second region is located in a direction away from the surface of the current collector, the thickness of the second region accounts for ½ of the thickness of the active material layer, and the binder content in the second region is denoted as B; the electrode sheet satisfies: 1<B/A≤1.04.
1 . A secondary battery including an electrode sheet, the electrode sheet including
a current collector; and
an active material layer provided on at least one surface of the current collector; the active material layer is divided into a first region and a second region in its thickness direction;
the first region is located in a direction close to the surface of the current collector, the thickness of the first region accounts for ½ of the thickness of the active material layer, and a binder content of the first region is denoted as A;
the second region is located in a direction away from the surface of the current collector, the thickness of the second region accounts for ½ of the thickness of the active material layer, and the binder content of the first region is denoted as B;
the electrode sheet satisfies: 1<B/A≤1.04.
2 . The secondary battery according to claim 1 , wherein the electrode sheet satisfies: 1.01<B/A≤1.03.
3 . The secondary battery according to claim 1 , wherein the thickness of the active material layer is 40 μm to 180 μm; optionally, the thickness of the active material layer is 60 μm to 100 μm.
4 . The secondary battery according to claim 1 , wherein,
a porosity of the first region is 25% to 30%; and/or,
a porosity of the second region is 25% to 30%.
5 . The secondary battery according to claim 1 , wherein a difference between a porosity of the first region and a porosity of the second region is ≤5%.
6 . The secondary battery according to claim 1 , wherein a porosity of the first region is the same as a porosity of the second region.
7 . The secondary battery according to claim 1 , wherein the active material layer is self-supporting.
8 . The secondary battery according to claim 1 , wherein a tensile strength of the active material layer is 0.03 MPa to 1 MPa.
9 . The secondary battery according to claim 1 , wherein the electrode sheet is a positive electrode sheet; in the active material layer, a binder includes at least one of polyvinylidene fluoride, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.
10 . The secondary battery according to claim 1 , wherein the electrode sheet is a negative electrode sheet; in the active material layer, a binder includes a polymer having a polar functional group.
11 . The secondary battery according to claim 10 , wherein a weight average molecular weight of the polymer is ≥200,000.
12 . The secondary battery according to claim 10 , wherein the polymer is selected from at least one of chain polymers and cross-network polymers.
13 . The secondary battery according to claim 10 , wherein the polymer is selected from at least one of polyacrylonitrile, polyacrylic acid, polyamide, acrylic acid-acrylonitrile copolymer and derivatives thereof, acrylic acid-acrylate copolymer and derivatives thereof, acrylic acid-acrylamide copolymer and derivatives thereof.
14 . The secondary battery according to claim 1 , wherein in the active material layer, a mass percentage of a binder is 0.5% to 5%.
15 . The secondary battery according to claim 1 , wherein the active material layer further includes an additive, and the additive includes at least one of polytetrafluoroethylene, polyethylene, polypropylene, and polyacrylonitrile.
16 . A method for preparing a secondary battery, comprising preparing an electrode sheet by the following steps:
preparing an electrode sheet slurry with a solid content greater than or equal to 65%;
extruding the electrode sheet slurry to prepare an active material layer; and
compounding the active material layer with a current collector to prepare the electrode sheet;
wherein an active material layer is provided on at least one surface of the current collector;
the active material layer is divided into a first region and a second region in its thickness direction;
the first region is located in a direction close to the surface of the current collector, the thickness of the first region accounts for ½ of the thickness of the active material layer, and a binder content of the first region is denoted as A;
the second region is located in a direction away from the surface of the current collector, the thickness of the second region accounts for ½ of the thickness of the active material layer, and the binder content of the first region is denoted as B;
the electrode sheet satisfies: 1<B/A≤1.04.
17 . The method for preparing a secondary battery according to claim 16 , wherein the electrode sheet is a negative electrode sheet, and the solid content of the electrode sheet slurry is 68% to 74%.
18 . The method for preparing a secondary battery according to claim 16 , wherein the electrode sheet is a positive electrode sheet, and the solid content of the electrode sheet slurry is 75% to 80%.
19 . An electrical apparatus, including the secondary battery according to claim 1 or the secondary battery prepared by a method for preparing a secondary battery according to claim 16 .